Modified Kernel Approach:
There is a rich collection of studies in which the underlying kernel is modified to work with ordinal or categorical variables. For example, [1]} considers the sum + product kernel; [2]} propose hybrid diffusion kernels, HyBO; and [3]} propose frequency modulated kernels. The BOCS algorithm [4]} for categorical variables uses a scalable modified acquisition function. [5]}, [6]}, [7]}, [8]} all use modified kernels to adapt the underlying surrogate surface.
Our approach is unique that any modified kernel can be incorporated into our framework for the solution of multi-objective mixed-variable problems. Currently we use the modified RBF kernel for modelling the surrogate surface, with our future research focused on different kernels in our framework.
